2.1. Clinical Importance of Uterine Leiomyomas
Leiomyomas are benign soft-tissue tumors that arise from smooth muscle tissue. Leiomyomas of the uterus are the most common, abnormal pelvic growth diagnosed in women. Leiomyomas are also called “myomas” and “uterine fibroids”. As benign, non-cancerous, growths arising from uterine smooth muscle (myometrium), leiomyomas are unrelated to the common forms of uterine cancer and uterine cervical cancer which typically arise from the uterine lining (endometrium) or cervical epithelium, respectively. In the United States, leiomyomas occur in the majority of all women (Flake et al., 2003, Environ Health Perspect. 111:1037-54). Leiomyomas are particularly prevalent in African-American women, who report a 3 times greater rate of occurrence than Caucasian women (Marshall et al., 1997, Obstet. Gynecol. 90:967-73). Although rare, leiomyomas also develop outside the uterus in both women and men. Extra-uterine sites of leiomyoma occurrence include the nipple, esophagus, scrotum, and seminal vesicles which all possess smooth muscle (Farman, 1975, S Afr Med J. 49:1333-40). In addition, rare, familial syndromes, including diffuse leiomyomatosis and Alport Syndrome, are associated with recurrent leiomyomas in multiple anatomic sites. Smooth muscle tumors are also common in the avian species, typically involving the oviduct, an analogous structure to the mammalian uterus. Japanese quail (Coturnix cturnix japonica) and the common chicken hen (Gallus domesticus) are especially affected, with prevalences varying up to 60% (Foster et al., 1989, Poult Sci. 68:1447-53; and Anjum et al., 1988, Res Vet Sci. 45:341-8). Despite their frequency, the pathobiology of leiomyomas remains poorly understood.
In women, leiomyomas contribute to a spectrum of symptoms including heavy, irregular, and prolonged menstrual bleeding and anemia. Leiomyomas may also cause pelvic discomfort, and bowel and bladder dysfunction from pressure on these adjacent structures. Leiomyomas have also been associated with infertility and recurrent abortion. The presence of leiomyomas can interfere with normal labor during the birth process, necessitating cesarean section. In addition to abnormal labor, leiomyomas restrict normal intra-uterine growth and predispose to postpartum hemorrhage secondary to uterine atony.
Histologically, leiomyomas arise from smooth muscle, show benign cell structure, and are distinct and unrelated to precancerous and cancerous cell growth affecting the uterine lining or endometrium. Leiomyomas arise from genetically similar clones of uterine smooth muscle cells, and they grow under the influence of local growth factors and in the presence of sex hormones. Evidence supports a more important contribution of progesterone than estrogen to myoma growth (Rein, 2000, Environ Health Perspect. 108 Suppl 5:791-3). The contribution of progesterone and estrogen to leiomyoma growth is uncertain, however, based on the observation that leiomyomas often recede in size during pregnancy, which is a time of high circulating estrogen and progesterone levels (Strobelt et al., 1994, J Ultrasound Med. 13:399-401). Adding to the uncertainty of the role of estrogen in myoma etiology, the clinical use of tamoxifen, an estrogen antagonist drug, has been associated with increased, not decreased, growth of leiomyomas (Schwartz et al., 1998, J Ultrasound Med. 17:699-703). Typically, leiomyomas in women appear after menarche, proliferate and grow during the reproductive years, and stabilize or regress after menopause. The diagnosis of leiomyomas is based on patient signs and symptoms, followed by physical and pelvic examination, demonstrating a pelvic mass, and confirmation by trans-abdominal or transvaginal ultrasonic visualization. The etiology and hormonal contributions to leiomyomas remain poorly understood.
Study of the biochemistry of uterine leiomyomas has shown that myoma tissue preferentially metabolizes estrogen to 4-hydroxy estrogen metabolites, demonstrating a different pattern of estrogen metabolism than surrounding normal myometrial smooth muscle (Liehr et al., 1995, Proc Natl Acad Sci USA 92:9220-4). Biochemical comparison of the extra-cellular matrix of leiomyoma tissue compared to surrounding normal tissue reveals differences in the composition and structure of collagen which may contribute to abnormal growth (Berto et al., 2003, Biochim Biophys Acta. 1619:98-112.)
Other than surgery, there are few safe and effective treatment options available to women with symptomatic leiomyomas. Gonadotropin-releasing hormone agonists (GnRH-a) inhibit steroidogenesis and induce pharmacologic menopause. Through this mechanism, GnRH-a's can reduce leiomyoma volume by 50% in 3 to 6 months. However, because these agents cause severe menopausal symptoms and the risk of estrogen-deficiency related bone loss (osteoporosis), these drugs cannot be used for prolonged periods of time. Moreover, leiomyomas tend to regrow after cessation of GnRH-a therapy. As a result, GnRH-a treatment, independent of subsequent surgery, is not recognized as an effective, long-term treatment of leiomyomas.
The surgical procedures for treatment of uterine leiomyomas are myomectomy and hysterectomy (Nair, 2003, Ann Acad Med. Singapore. 32:615-23). Myomectomy, done either through a laparotomy or laparoscopy, is performed to remove the leiomyoma and conserve the uterus. This is usually attempted in young women who may desire future pregnancy. Unfortunately, myomectomy is followed by extensive pelvic adhesions that themselves can reduce future fertility. Additionally, if the leiomyoma penetrates the uterine cavity, any future pregnancy after myomectomy carries an increased risk of uterine rupture and delivery has to be accomplished by cesarean section.
Hysterectomy remains the definitive surgical treatment for leiomyomas. Symptomatic uterine leiomyomas account for approximately one third of all hysterectomies performed among middle-aged women (Nair, 2003, Ann Acad Med. Singapore. 32:615-23). The impact of this surgical approach to leiomyomas is extremely costly considering the long postoperative time and recuperation away from work. There are also well known complications to hysterectomy. These complications include postoperative hemorrhage, fever, or injury to adjacent organs.
Two recent modalities have been developed for less extreme interventional treatment of uterine fibroids: myolysis and uterine artery embolization (Lefebvre et al., 2003, J Obstet Gynaecol Can. 25:396-418). Myolysis refers to the technique of disrupting or abolishing the blood supply to the fibroid causing shrinkage by using bipolar or monopolar electrosurgery. It is only applicable if there are less than three fibroids present and/or the largest one measures less than 10 cm in diameter. The procedure is also not recommended for women who wish to get pregnant, since the risk of uterine rupture is high. Uterine artery embolization (UAE) is a procedure done by radiologists with the objective of eliminating the blood supply to leiomyoma tissue. After some months following the treatment, UAE typically results in an average reduction of myoma tissue volume of about 50%. However, acutely causing the death of myoma tissue due to arterial blockage has side effects. The procedure can be followed by severe pain requiring hospitalization. Some concern about future fertility has been raised following UAE, as well as lack of ability to treat all leiomyomas present. A portion of women undergoing uterine artery embolism develop subsequent amenorrhea and menopause due to inadvertent impairment of ovarian function (Spies et al., 2002, Obstet. Gynecol. 100:873-80).
For women with symptomatic leiomyomas, who wish to preserve fertility or avoid surgery, more conservative, more effective, and safer methods of medical treatment are needed. Ideally, improved medical treatments to manage leiomyomas will preserve an intact uterus, better preserve fertility, and, as adjunct treatments, improve the safety and long-term efficacy of more conservative treatment modalities such as UAE and laparoscopic myomectomy.
2.2. Biologic Activities of Cruciferous Indoles
Cruciferous vegetables contain a family of plant protective compounds called glucobrassicins which give rise to active compounds with the indole molecular ring, exemplified by indole-3-carbinol (I3C). However, I3C is highly unstable in water and acid. When given orally, I3C generates a number of gastric reaction products with a variety of biologic actions (De Kruif et al., 1991, Chem Biol Interact; 80:303-15). These products are highly enzyme inducing and associated with both the inactivation and activation of carcinogens. As such, the use of I3C has been associated with both the growth inhibition and growth promotion in experimental cancers. In addition, unwanted enzyme induction by I3C reaction products following oral I3C use may alter the metabolism of other drugs, steroid hormones including estrogen, and contraceptives raising safety concerns. Oral use of I3C in humans has been shown to increase production of the 4-hydroxy estrogen metabolites previously associated with leiomyoma tissue (Michnovicz et al., 1997, J Natl Cancer Inst. 89:718-23). In addition, I3C's use is associated with a number of safety concerns due to its enzyme-inducing and reproductive-toxic actions making it unacceptable for use in women of reproductive age (Dashwood, 1998, Chem Biol Interact. 110:1-5; and Gao et al., 2002, Toxicol Appl Pharmacol. 183:179-88).
One prominent product derived from I3C, and also present in cruciferous plants is 3,3′-diindolylmethane (DIM), the linear dimer molecule formed from the condensation of two molecules of I3C. Once formed, DIM is stable in acid and less enzyme inducing than other I3C products (Bradfield et al., 1987, J Toxicol Environ Health. 21:311-23). In cell culture, DIM has been shown to have apoptosis promoting effects in both estrogen-dependent and independent breast cancer cells (Hong et al., 2002, Biochem Pharmacol 63:1085-97). DIM has also been shown to specifically induce apoptosis in papillomavirus altered cervical cancer cell lines (Chen et al., 2001, J Nutr. 131:3294-302). In animals, orally administered DIM inhibits the growth of certain chemically induced forms of breast cancer (Chen et al., 1998, Carcinogenesis, 19:1631-9).
Investigations of DIM have resulted in U.S. Pat. No. 5,948,808, “Indole-3-carbinol, diindolylmethane and substituted analogs as antiestrogens”, which provides for a method of treating estrogen-dependent cancer. U.S. Pat. No. 6,656,963, “Indole-3-carbinol (I3C) derivatives and methods”, discloses additional derivatives of I3C for use in methods to inhibit cancerous cell growth, but specifically excludes DIM.
Previous experimental work by the present inventor has described the use of DIM and the related trimeric derivative of I3C, 2-(Indol-3-ylmethyl)-3,3′-diindolylmethane (LTR), in specialized formulations (U.S. Pat. No. 6,086,915) and in treatments for breast pain (mastalgia) and endometriosis (U.S. Pat. No. 6,689,387). Endometriosis is a disorder of uterine epithelial tissue (endometrium) which migrates outside the endometrial cavity of the uterus and resumes growth, typically in the abdomen. Pending applications of the present inventor also include uses of DIM and LTR for cervical dysplasia (U.S. patent application Ser. No. 10/616,477), and for Human Papilloma Virus (HPV) infections (U.S. patent application Ser. No. 10/616,477). Like endometriosis, cervical dysplasia and HPV infections are disorders of epithelial tissue and not smooth muscle. Leiomyomas are a distinct pathobiologic entity, arising only in uterine or extra-uterine smooth muscle which is a distinct tissue with different appearance, structure, function and embryologic origin than endometrium and other epithelial tissue.
A more recent patent application (U.S. Patent Application Publication No. 2003/0220377, filed May 7, 2003) describes synthetic indole anti-estrogenic compounds, structurally unrelated to DIM, which are proposed to treat both cancerous and benign conditions involving the uterus. In distinction to these synthetic, indole anti-estrogens, DIM has been shown to have estrogenic, growth promoting activity in breast cancer cells (Riby et al., 2000, Biochem Pharmacol. 60:167-77) and estrogen-receptor activating activity in endometrial cancer cells (Leong et al., 2004, Mol. Endocrinol. 18:291-302. Epub 2003 Nov. 26). Finally, U.S. Patent Application Publication No. 2001/0002393 (filed Dec. 20, 2000), describes methods and kits for treating and diagnosing leiomyomas using inhibitors of metalloproteinase enzymes.
It would be beneficial to have new therapeutic options for leiomyoma treatment that are non-invasive, that avoid or minimize surgery, and that avoid the side effects of systemically administered hormonal therapies. New medical therapies for the treatment leiomyoma-related conditions are needed.